1. Field of the Invention
The invention is directed to an improved fuel injection valve for internal combustion engines.
2. Description of the Prior Art
A fuel injection valve of the type with which this invention is concerned is known from the reference DE 199 42 370 A1. In this fuel injection valve, a valve needle is disposed so that it can move longitudinally in the bore of a valve body; a pressure chamber, which can be filled with highly pressurized fuel, is embodied between the wall of the bore and the valve needle. A number of injection openings are embodied in the valve body at the combustion chamber end of the bore and connect the bore to the combustion chamber of the engine. A conical valve seat is also embodied at the end oriented at the combustion chamber and a valve sealing surface of the valve needle comes into contact with this conical valve seat when the valve needle is in the closed position. In the closed position of the valve needle, the fuel cannot flow from the pressure chamber to the injection openings. When the valve needle lifts away from the valve seat, fuel flows out of the pressure chamber, between the valve sealing surface and a valve seat, to the injection openings, and from there, is injected into the combustion chamber of the engine.
In order to achieve a reliable seal against the valve seat, the valve sealing surface has two conical surfaces; the first conical surface is disposed upstream of the second conical surface and the two conical surfaces adjoin each other directly. The opening angle of the first conical surface here is smaller than the opening angle of the valve seat, which is in turn smaller than the opening angle of the second conical surface. As a result, at the transition of the two conical surfaces, an annular edge is produced, which comes to rest against the valve seat in the closed position of the valve needle and produces a favorably tight seal due to the relatively high surface pressure.
The hydraulic pressure acting on parts of the valve sealing surface moves the valve needle in the bore counter to a closing force directed toward the valve seat. The pressure at which the valve needle just begins to lift up from the valve seat is referred to as the opening pressure. This opening pressure depends on hydraulically effective seat diameter of the valve needle against the valve seat, which with the above-described geometry, corresponds to the diameter of the sealing edge. However, this is only true as long as no deformations of the valve needle and valve seat occur. During operation, the valve needle always deforms the valve sealing surface elastically and, particularly after extended operation, deforms the valve sealing surface plastically. As a result, the hydraulically effective seat diameter of the valve needle can change over time and therefore so can the opening pressure. In order to counteract this, the reference DE 196 34 933 A1 has disclosed providing an annular groove in the valve needle between the two conical surfaces of the valve sealing surface. However, this has the disadvantage of reducing the rigidity of the valve needle, which can lead to a deformation of the valve needle in the vicinity of the annular groove. This would jeopardize the functional performance of the entire fuel injection valve.
The fuel injection valve according to the invention has the advantage over the prior art of maintaining the hydraulically effective diameter of the valve needle against the valve seat over the entire service life without reducing the rigidity of the valve needle. To this end, two parallel annular grooves are provided in the valve seat, which respectively extend in radial planes in relation to the longitudinal axis of the bore. The valve needle in this case rests against the valve seat between the two annular grooves. This delimits the surface area of the valve seat against which the valve needle rests and therefore also delimits the hydraulically effective seat diameter of the valve needle.
In an advantageous embodiment of the subject of the invention, the differential angle between the first conical surface and the conical valve seat is greater than the differential angle between the second conical surface and the valve seat. This further encourages the constancy of the hydraulically effective seat diameter.
In another advantageous embodiment, the first annular groove is embodied as an end facing or wall of the bore. This permits the first annular groove to be easily produced with high precision. In this instance, it is particularly advantageous that the first annular groove remains continuously connected to the pressure chamber without further steps being required so that the fuel pressure in the pressure chamber acts on the valve sealing surface at all times.